1. Field of the Invention
The present invention relates to electronic cameras that perform image pickup processings, specifically, correction processings on image data, and exposure control at the time of photographing.
2. Description of the Related Art
A typical electronic camera performs a variety of correction processings such as white balance adjustment, gray level correction, color correction on image data outputted from the image sensor, in order to obtain an image adapted to the various conditions of a subject (for example, a light source illuminating the subject, contrast and so on), Some conventional electronic camera includes a color temperature determining part that determines the color temperature of a light source illuminating a subject. Such electronic camera achieves a white balance adjustment (in some instances, color correction) using the determined color temperature as a control parameter.
Also, another conventional electronic camera includes a contrast determining part that determines the contrast of a subject, and implements a gray level correction using the determined contrast as a control parameter.
These electronic cameras determine the latest color temperature and contrast of an image at the time when the release button is pressed down or immediately before that. Conventionally, the correction processings are implemented according to the latest color temperature and contrast. In such a case, when conditions of a subject vary during continuous shooting, the correction processings are performed in accordance with the variations of the subject.
However, there is a case where the position of the subject shifts even during the continuous shooting of the same subject, resulting in causing the color temperature determined by the electronic camera to vary. This causes a problem that the white balance of the same subject varies among a plurality of images. If these images are sequentially reproduced, the user may feel the images very unnatural.
Especially, a subject having a red color is very susceptible to the white balance adjustment. Therefore, the above problem is significant when a red moving car, for example, is continuously shot within an angle of field. Similar problems occur not only in performing the white balance adjustment but also in the gray level correction and color correction.
In order to obtain stable results of the correction processings, some conventional methods have been contrived which limits the variation values of control parameters within a predetermined range.
However, such methods are disadvantageous in that when the conditions of a subject distinctively change, for example, when a car is moving from a sunny place to a shady place or vise versa, it is very hard to perform the correction processings in accordance with such variations.
Some electronic cameras each perform exposure controls (including gain adjustment to analog image signals) with a high adaptability, based on the brightness repetitively determined by a photometric sensor or the like. Such electronic cameras, however, disadvantageously perform exposure control in accordance with such a variation even in the case where the conditions of a subject temporarily vary irrespective of the user's intention during a course of his/her continuous shooting of the same subject.
As explained above, there have been unsolved problems in the conventional image pickup processings (particularly, correction processings and exposure controls) that enhancing the stability of the processings will degrade adaptability thereof, while enhancing the adaptability will degrade the stability.